1 #include <iostream>
  2 #include <stdio.h>
  3 #include <map>
  4 #include <memory.h>
  5 #include <vector>
  6 using namespace std;
  7 
  8 
  9 const int maxn = 10000 + 10;
 10 int low[maxn],pre[maxn],dfs_clock=0;
 11 map<int,bool> isbridge;
 12 vector<int> G[maxn];
 13 int cnt_bridge;
 14 int father[maxn];
 15 
 16 int getid(int u,int v)
 17 {
 18     return u*10000+v;
 19 }
 20 
 21 int dfs(int u, int fa)
 22 {
 23     father[u]=fa;
 24     int lowu = pre[u] = ++dfs_clock;
 25     int child = 0;
 26     for(int i = 0; i < G[u].size(); i++)
 27     {
 28         int v = G[u][i];
 29         if(!pre[v])   // 没有访问过v
 30         {
 31             child++;
 32             int lowv = dfs(v, u);
 33             lowu = min(lowu, lowv); // 用后代的low函数更新自己
 34             if(lowv > pre[u]) // 判断边(u,v)是否为桥
 35             {
 36                 isbridge[getid(u,v)]=isbridge[getid(v,u)]=true;
 37                 cnt_bridge++;
 38             }
 39         }
 40         else if(pre[v] < pre[u] && v != fa)
 41         {
 42             lowu = min(lowu, pre[v]); // 用反向边更新自己
 43         }
 44     }
 45     return low[u]=lowu;
 46 }
 47 
 48 void init(int n)
 49 {
 50     isbridge.clear();
 51     memset(pre,0,sizeof pre);
 52     cnt_bridge=dfs_clock=0;
 53     for(int i=0; i<n; i++)
 54     {
 55         G[i].clear();
 56     }
 57 }
 58 
 59 
 60 bool vis[maxn];
 61 int cnt;
 62 int dfs_conn(int u)
 63 {
 64     vis[u]=true;
 65     cnt++;
 66     for(int i=0;i<G[u].size();i++)
 67     {
 68         int v=G[u][i];
 69         if(!vis[v])
 70             dfs_conn(v);
 71     }
 72 }
 73 
 74 bool isconn(int n)
 75 {
 76     memset(vis,false,sizeof vis);
 77     cnt=0;
 78     dfs_conn(0);
 79     return cnt==n;
 80 }
 81 
 82 
 83 int main()
 84 {
 85     #ifndef ONLINE_JUDGE
 86     freopen("in.txt","r",stdin);
 87     #endif
 88 
 89     int T;
 90     cin>>T;
 91     while(T--)
 92     {
 93         map<string,int> id;
 94         map<int,string> id2;
 95         vector<int> edges;
 96         int n,m;
 97         scanf("%d %d",&n,&m);
 98         init(n);
 99         int num=0;
100         for(int i=0;i<m;i++)
101         {
102 
103             char str1[20],str2[20];
104             scanf("%s %s",str1,str2);
105             int a,b;
106             if(id.count((string)str1)>0)
107             {
108                 a=id[(string)str1];
109             }
110             else
111             {
112                 a=id[(string)str1]=num++;
113             }
114 
115             if(id.count((string)str2)>0)
116             {
117                 b=id[(string)str2];
118             }
119             else
120             {
121                 b=id[(string)str2]=num++;
122             }
123 
124             id2[a]=(string)str1;
125             id2[b]=(string)str2;
126 
127             G[a].push_back(b);
128             G[b].push_back(a);
129             edges.push_back(getid(a,b));
130         }
131 
132         if(!isconn(n))
133         {
134             puts("0");
135             continue;
136         }
137 
138         dfs(0,-1);
139         cout<<cnt_bridge<<endl;
140         for(int i=0;i<edges.size();i++)
141         {
142             if(isbridge[edges[i]])
143             {
144                 printf("%s %s\n",id2[edges[i]/10000].c_str(),id2[edges[i]%10000].c_str());
145             }
146         }
147     }
148 
149     return 0;
150 }